Polyetheramines are used widely used as curing agents for epoxy resins or as raw materials in the synthesis of polyamides or polyureas. Such polyetheramines are generally produced by the reaction of an alkylene oxide with an alcohol to form a polyoxyalkylene polyol and then subsequent conversion of the hydroxyl groups to amine groups by reductive amination.
For example, U.S. Pat. No. 3,654,370 describes a process in which a polyoxyalkylene polyol is treated with ammonia and hydrogen in the presence of a nickel oxide, copper oxide and chromium oxide catalyst to form a mixture of polyetheramines. U.S. Pat. No. 4,766,245 further describes a process in which high molecular weight polyoxyalkylene amines are produced by contacting high molecular weight polyoxyalkylene polyols with ammonia in the presence of hydrogen and a Raney nickel/aluminum catalyst. Additionally, U.S. Pat. No. 4,769,438 describes a process in which a propoxylated 1,4-butanediol is first aminated using a Raney nickel catalyst and then subsequently converted to an adduct by a reaction with a small amount of an epoxy resin. Finally, U.S. Pat. No. 7,550,550 describes a process for producing hindered polyetherdiamines and polyethertriamines by reductive animation of a variety of polyoxyalkylene polyols.
One drawback to polyetheramines produced by known processes is that they are formed from polyols having polyether groups in the polyol backbone. When used as a curing agent for epoxy resins, these polyether groups provide good flexibility in the cured resins, but also cause a significant reduction in their thermal properties. Attempts to reduce the amount of polyether groups in the polyol backbone by utilizing diols such as diethylene glycol and dipropylene glycol have proven unsuccessful, since these materials tend to undergo unwanted intramolecular side reactions during reductive amination to form large amounts of secondary amines, such as morpholine and 3,5-dimethyl morpholine, and only minor amounts of bis(aminoethyl)ether and bis(aminopropyl)ether.
Another drawback to current curing agents is the high temperatures typically required to cure these systems. For example, conventional hardener systems with cycloaliphatic diamines such as isophorone diamine, typically required 70° C. to 80° C. to cure. Heating a large mold from ambient temperature to 70° C. to 80° C. may take 3-4 hours, resulting in a slower manufacturing time.
Thus, needs exist for new amine curing agents that provide good flexibility and good thermal properties in the cured resin, as well as easily implemented processes for their production. Also, needs exist for new curing agents that have improved cure performance, such as allowing for curing at lower temperatures or for shorter periods of time.